Solar cells, also termed photovoltaic or PV cells, convert sunlight into electricity. Traditionally, these electronic devices have been fabricated using silicon (Si) as a light-absorbing, semiconducting material in a relatively expensive production process. To make solar cells more economically viable, solar cell device architectures have recently been developed that use thin-film, light-absorbing semiconductor materials such as copper-indium-gallium-sulfo-di-selenide, also termed CIGS.
Despite the demonstrated potential of CIGS in thin-film solar cells, the toxicity and low abundance of indium and selenium are major impediments to the widespread use and acceptance of CIGS in commercial devices. Attractive alternatives to CIGS include quaternary chalcogenides, particularly copper zinc tin sulfide, Cu2ZnSnS4 (CZTS). It has a bandgap of about 1.5 eV, well within the solar spectrum, and an absorption coefficient greater than 104 cm−1. In addition, the CZTS elements are non-toxic and abundant.
Currently, the development of solar cells based upon CZTS lags significantly behind CIGS-based solar cells. Thin films of CZTS have been prepared via sputtering of Cu, SnS, and ZnS precursors, hybrid sputtering, pulsed laser deposition, spray pyrolysis of halides and thiourea complexes, electrodeposition/thermal sulfurization, E-beam Cu/Zn/Sn/thermal sulfurization, and sol-gel followed by thermal sulfurization. However, these methods so not lend themselves to the precision of screen-printing, and also suffer from a lack of reproducibility of film heights and film homogeneity. Delamination of the CZTS layer has also been observed.
Therefore, there is a need for quaternary chalcogenide compositions which can be screen-printed on a substrate, and subsequently converted to an absorber film for use in a photovoltaic device.